Air strikes hit rebel-held positions near the Syrian capital and outside the northern city of Aleppo, hours before a deadline for a landmark cease-fire in the country's nearly five-year civil war.

The cease-fire brokered by the United States and Russia is due to go into effect at midnight local time.

Both Syrian President Bashar al-Assad and the main opposition body have agreed to the deal -- which allows fighting to continue against the Islamic State group and the Al-Nusra Front, Al-Qaeda's branch in Syria.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said the Syrian government and its ally Russia had launched a wave of attacks on rebel areas ahead of the deadline.

"It's more intense than usual. It's as if they want to subdue rebels in these regions or score points before the cease-fire," Observatory head Rami Abdel Rahman said.